1. Technical Field of the Invention
The present invention relates to an exhaust gas treatment system for treating exhaust gas containing organic component, such as exhaust gas generated from a painting facility, a semiconductor/electronic component manufacturing factory, etc. More particularly, the invention relates to such exhaust gas treatment system adapted for treating the exhaust gas by oxidizing/decomposing the organic component contained in the gas.
2. Description of the Related Art
For oxidizing/decomposing an organic component contained at a low concentration in exhaust gas to clean the exhaust gas and also recovering the heat generated in association with the decomposition for use as an energy source for running the factory (e.g., as energy source for the main production activity of the factory), there have been proposed and practiced a variety of schemes as follows. According to one such scheme, the organic component in the exhaust gas is condensed by means of a condensing device to produce condensed gas having an enhanced concentration of organic component. Then, this condensed gas is charged into a combustion device adapted for exhaust gas treatment, such as direct combustion type, catalytic combustion type, regenerative combustion type device, etc., so that the organic component is combusted therein, and the heat retained in the resultant combustion exhaust gas (i.e., cleaned gas) from the combustion device is recovered through a heat exchanger. According to another scheme, the treatment-object exhaust gas or the condensed gas thereof is fed, together with oxygen-containing combustion gas, to a burner of a boiler used as the heat source of the factory, so that the organic component therein is combusted and the heat generated during the oxidation/decomposition of the organic component in the exhaust gas is collected in the form of steam generated from the boiler.
The prior art has proposed still another scheme whose implementing system is illustrated in FIG. 4. It is said that this scheme, in addition to the oxidation/decomposition of the organic component in the exhaust gas, provides a further advantage over the above-described schemes by allowing even more efficient utilization of the decomposition heat (ie., the chemical energy present within the organic component in the exhaust gas) for the factory operation. More particularly, in the system implementing this scheme, treatment-target exhaust gas A is charged, as the oxygen-containing combustion gas, into a gas engine 30 together with a fuel G so as to run this engine 30. Then, the organic component in the gas A will be subjected to oxidation/decomposition process during the combustion process in the engine 30. Further, a generator 31 is driven by the output of this engine to generate electric power E which in turn is used for the main factory operation; and also the heat retained in engine exhaust gas D exhausted from the engine 30 is recovered by a heat exchanger 32 to be used as heat source which is to be used also for the main factory operation.
With the above-described exhaust gas treatment system utilizing a gas engine (i.e., a so-called xe2x80x9cco-generation systemxe2x80x9d modified to act also as an exhaust gas treatment system), the oxidation/decomposition heat of the organic component is recovered in the form of electric power E. Thus, compared with the conventional systems in which the oxidation/decomposition heat of the organic component in exhaust gas is recovered in the form of heat recovered from the combustion exhaust gas or steam generated from a boiler, the above system may utilize the oxidation/decomposition heat of the organic component of exhaust gas more efficiently as energy source for factory operation. Hence, enhanced energy saving and further reduction in CO2 generation may be obtained.
With such gas engine, however, its intake amount of oxygen-containing combustion gas (i.e., combustion air) is rather limited. Thus, according to such exhaust gas treatment system using a gas engine, even if this system employs the scheme of feeding the condensed gas which has its organic component concentration enhanced and its amount reduced by a condensing device to the gas engine 30 as the oxygen-containing combustion gas therefor, it is difficult for this system to efficiently treat a large amount of exhaust gas with a low concentration of organic component generated from a painting facility or semiconductor/electronic component manufacturing factory. For this reason, in those factories which generate a relatively large amount of exhaust gas needing treatment, as illustrated in FIG. 5, if a co-generation system using a gas engine (i.e., a system in which a generator 31 is driven by a gas engine 30 and heat retained in the exhaust gas D from the engine is recovered through a heat exchanger 32) is to be implemented for achieving higher energy saving and CO2 generation reducing effects, this is feasible only through the conventional scheme in which condensed gas Bxe2x80x2 with organic component concentration enhanced through a condensing device 1 is introduced into an exhaust-gas treating combustion device 33 for combustion of the organic component therein (or through the alternative conventional scheme, illustrated in this FIG. 5 by broken lines, in which only a portion of the exhaust gas A to be fed to the exhaust-gas treating combustion device 33 or condensed gas Bxe2x80x2 thereof is fed to the gas engine 30 as its oxygen-containing combustion gas).
In view of the above-described state of the art, a primary object of the present invention is to provide an exhaust gas treatment system capable of achieving efficient treatment of a large amount of exhaust gas by recovering oxidation/decomposition heat of organic component in the exhaust gas in the form of electric energy as well as equivalent or higher energy saving effect and CO2 generation reducing effect as compared with the conventional exhaust gas treatment system using a gas engine.
For fulfilling the above-noted object, according to the present invention, an exhaust gas treatment system comprises:
a condensing device for condensing an organic component contained in exhaust gas to be treated so as to produce condensed gas with an enhanced organic component concentration;
a gas turbine for receiving the condensed gas from the condenser device as oxygen-containing combustion gas and then generating power; and
a generator operable to receive the power from the gas turbine for generating electric power.
Compared with a gas engine of an equivalent output, a gas turbine allows a larger intake of oxygen-containing combustion gas. Therefore, if the gas turbine is driven by both fuel and the exhaust gas as its oxygen-containing containing combustion gas, the gas turbine can treat a large amount of exhaust gas by oxidizing and decomposing the organic component in the exhaust gas through its combustion therein in a more efficient manner than the above-described gas-engine type system shown in FIG. 4; and heat generated in association with the oxidization/decomposition process may be recovered in the form of electric energy from the generator driven by the gas turbine.
Such gas turbine, however, consumes a larger amount of fuel than a gas engine of equivalent output. Therefore, if exhaust gas with a relatively low organic component concentration (e.g., exhaust gas with an organic component concentration ranging 100 to 500 ppm approximately), such as the exhaust gas generated from a painting facility or semiconductor/electronic component manufacturing factory, is directly fed to the gas turbine as the oxygen-containing combustion gas, the reduction in the fuel consumption amount enabled by the introduction of the organic component of the exhaust gas will be rather limited, so that the fuel consumption amount of the entire system will be still greater than the conventional gas-engine type treatment system and its energy saving effect and CO2 generation reducing effect will be low or unsatisfactory correspondingly.
Then, according to the system of the present invention described above, the system includes a condensing device for condensing an organic component contained in exhaust gas to be treated so as to produce condensed gas with an enhanced organic component concentration. Then, if this condensed gas generated from this condenser device is supplied to the gas turbine as the oxygen-containing combustion gas, the gas turbine, due to its larger intake of combustion gas, can receive a significantly greater amount of organic component than the case when the turbine directly receives a same amount of non-condensed exhaust gas as the condensed gas. Consequently, the system can treat an even greater amount of exhaust gas and at the same time the fuel consumption amount of the generator per unit electric power generation amount may be reduced effectively. Therefore, this system of the invention achieves substantially same or even higher energy saving effect and CO2 generating reducing effect, compared not only with the conventional system of FIG. 5 implementing the co-generation scheme using a gas engine, but also the system in which the exhaust gas is directly supplied to a gas engine as oxygen-containing combustion gas, or the conventional system of FIG. 4 in which condensed gas with organic component concentration enhanced through a condensing device is supplied to a gas engine as oxygen-containing combustion gas.
Further, exhaust gas from such gas turbine has a higher temperature than exhaust gas from a gas engine. Then, if the heat retained in the turbine exhaust gas is recovered during the above-described gas turbine operation using the condensed gas as oxygen-containing combustion gas, much greater amount of heat can be recovered in the form of high-temperature (hence, of greater utility) heat than the conventional system recovering the heat from gas engine exhaust gas. In this respect too, the energy saving effect and CO2 generation reducing effect may be further promoted.
As described above, the system of the invention achieves efficient treatment of a large amount of exhaust gas with a low organic component concentration as well as higher energy saving effect and CO2 generation reducing effect. Moreover, in comparison with the conventional exhaust gas treatment system of FIG. 5 implementing the co-generation scheme, the system of the invention can achieve also overall system cost reduction by eliminating the combustion device 33 required by the conventional system.
For ensuring the substantially same or higher energy saving effect and CO2 generation reducing effect, it is preferred that the condensed gas to be fed to the gas turbine as oxygen-containing combustion gas has an organic component concentration of 3000 ppm or higher.
Also preferably, the condensing device comprises an adsorbing-desorbing device by effecting an adsorbing step for adsorbing the organic component of the exhaust gas onto an adsorbent layer by causing the gas to pass the adsorbent layer and a desorbing step for desorbing the adsorbed organic component into a desorbing gas, which is smaller in its amount than the exhaust gas, by causing desorbing gas to pass the adsorbent layer after the adsorbing step, the device effecting the adsorbing step and the desorbing step for a plurality of cycles, so that the desorbing gas delivered from the adsorbent layer during the desorbing step is collected as the condensed gas to be discharged from the condensing device.
With the above-described adsorbing-desorbing type condensing device, with execution of repeated cycles of the adsorbing step and the subsequent desorbing step, the organic component in the exhaust gas is transferred from the exhaust gas into the smaller amount of desorbing gas, so that the organic component in the gas is concentrated to produce the condensed gas (i.e., the desorbing gas delivered from the adsorbent layer during the desorbing step) with enhanced concentration of organic component. This type of adsorbing-desorbing device is already in wide use in the above-described conventional exhaust gas treatment systems using a combustion device for exhaust gas treatment. Hence, in implementing the exhaust gas treatment system (i.e., system including a gas turbine) of the invention, if such adsorbing-desorbing type device is employed as the condensing device and the condensed gas produced by this device is supplied to the gas turbine as its oxygen-containing combustion gas, the system can be readily implemented by utilizing such commonly used adsorbing-desorbing type device and such implemented system will provide advantage of high reliability also.
Still preferably, the adsorbing-desorbing type condensing device is adapted to effect the adsorbing step and the desorbing step in parallel and continuous manner (e.g., a rotary adsorbing-desorbing device including an adsorbing rotor having an adsorbent layer with a plurality of adsorbing areas and desorbing areas alternatively arranged along a rotational path of the rotor, or a multi-adsorbing tower type device for selectively effecting the adsorbing step or desorbing step for each adsorbent layer by e.g., effecting the adsorbing step at one or some of the adsorbing layers while effecting the desorbing at another or other adsorbing layers at the same time). With this, the condensing device can continuously supply the condensed gas to the gas turbine as the oxygen-containing combustion gas.
Still preferably, in the exhaust gas treatment system of the invention, the adsorbing-desorbing type condensing device includes a sorting means for sorting the desorbing gas delivered from the adsorbent layer during the desorbing step between an earlier passage gas which passed the adsorbent layer at an earlier stage of the desorbing step and a later passage gas which passed the adsorbent layer at a later stage of the desorbing step and for subsequently causing the earlier gas, as an additional portion of the exhaust gas, to pass the adsorbent layer again at a subsequent adsorbing step while allowing the later passage gas to be discharged directly as the condensed gas.
With the above-described construction, by the sorting means, the desorbing gas delivered from the adsorbent layer during the desorbing step is sorted between the earlier passage gas which passed the adsorbent layer at an earlier stage of the step when the temperature of the adsorbent layer is still low and the efficiency of the desorption of the condensation-target component therefrom is also correspondingly low and the later passage gas which passed the adsorbent layer at a later stage of the step when the adsorbent layer has been heated to a sufficiently high temperature and the efficiency of the desorption of the target component therefrom is also correspondingly high. Consequently, the desorbing gas is sorted between a desorbing gas portion (i.e., earlier passage gas) delivered from the adsorbent layer with low or insufficient organic component concentration and a further desorbing gas portion (i.e., later passage gas) delivered from the adsorbent layer with high or sufficient organic component concentration.
Then, the earlier passage gas, because of its low organic component concentration, is caused to pass, as an additional portion of the treatment-object exhaust gas, again the adsorbent layer, so that the organic component contained therein is adsorbed to the adsorbent layer and then this adsorbed component is desorbed in the subsequent desorbing step into the small amount and higher temperature desorbing gas. On the other hand, the later passage gas delivered from the adsorbent layer with a high organic component concentration is directly collected as the condensed gas product and fed to the gas turbine as the oxygen-containing combustion gas.
That is to say, the earlier passage gas delivered from the adsorbent layer with low or insufficient organic component concentration is subjected to the condensing process again; and only the later passage gas delivered from the adsorbent layer with high or sufficient organic component concentration is collected as the condensed gas. With this, compared with a construction collecting the entire amount of the desorbing gas delivered from the adsorbent layer during the desorbing step, the concentration rate of the organic component in the exhaust gas may be effectively enhanced while avoiding adverse effect of the earlier sage of the desorbing step when the desorbing efficiency is still low (in this respect, see the U.S. application Ser. No. 09/532,252 filed on Mar. 22, 2000 by the same applicant). As a result, the concentration of the organic component in the condensed gas to be supplied as the oxygen-containing combustion gas to the gas turbine may be effectively enhanced and the energy saving effect and the CO2 generation reducing effect of the exhaust gas treatment system according to the invention may be further promoted
Incidentally, with appropriate setting of the xe2x80x9csorting point or timingxe2x80x9d where the earlier passage gas and the later passage gas are sorted from each other, since the concentration of the organic component in the earlier passage is rather low and also since the desorbing gas is smaller in its amount and the earlier passage gas is even smaller in its amount, the addition of this earlier passage gas to the exhaust gas as an additional portion thereof, when caused to pass the adsorbent layer in the adsorbing step, will not cause any significant increase in the processing load in the adsorbing process, so that resultant reduction in the adsorbing capacity for the organic component in the exhaust gas may be kept minimal. Hence, the adsorbing capacity for the organic component in the exhaust gas may be maintained sufficiently high without requiring physical enlargement of the adsorbent layer.
That is to say, provided that the conventional condensing device originally provides a concentration rate on the order of 20 times, this device, if modified with the addition of the sorting means will be able to readily provide a concentration rate on the order of 40 times.
Preferably, in the exhaust gas treatment system of the invention, the condensing device is capable of providing a concentration rate of 30 times or more of the organic component in the exhaust gas.
Namely, when the exhaust gas having an organic component concentration of 100 to 500 ppm approximately, such as exhaust gas generated from a painting facility or semiconductor/electronic component manufacturing factory, is to be treated by the exhaust gas treatment system of the present invention, with use of such condensing device capable of providing a concentration rate of 30 times or more of the organic component in the exhaust gas, the system will be able to stably maintain substantially same or even higher energy saving effect and CO2 generation reducing effect as or than the conventional system using a gas engine, irrespectively of slight variation in the organic component concentration in the exhaust gas to be treated.
Alternatively, for the purpose of feeding, to the gas turbine as the oxygen-containing combustion gas, the condensed gas having organic component concentration enhanced by the condensing device, the system may include a plurality of such condensing devices (e.g., a plurality of adsorbing-desorbing type devices) for effecting the concentration process of the organic component in multiple of steps for increasing the concentration rate in step-by-step manner.
Further and other objects, features and advantages of this invention will become apparent from the following detailed description of the preferred embodiments thereof with reference to the accompanying drawings.